Although gram negative bacillemia has become a life-threatening complication of the management of the immunologically "compromised" host, there is a paucity of information on the functional status of specific components of host defenses against bacterial invasion, the role of microbial products during the acute stages of infection in man, and the relationship of these factors to the pathophysiologic events that are observed clinically. In the continuation of this study at the UCLA Medical Center we will focus on: 1) prospective evaluation of human neutrophil function near the onset of bacteremia due to gram negative rods, particularly Klebsiella-Enteobacter, Serratia, and Ps. aeruginosa. We will use a new "miniaturized" leukocyte function test, granulocyte chemiluminescence, to evaluate simultaneously intrinsic neutrophil bactericidal function and humoral opsonic activity. (2) Refine radioimmunoassay methods, already achieved in principle, for quantitating 2 important bacillary antigens, the "Re" chemotype "core" glycolipid of Enterobacteriaceae and the K-1 antigen of E. Coli. Such tools will be used to attempt detection of circulating bacterial antigens at the onset of bacteremia by screening plasmas obtained simultaneously with culture positive blood. Additionally, they can be modified and employed to quantitate, by radiometric techniques, the humoral immune response to these antigens during the course of infection. (3) Measurement of other factors, such as immune complexes (by polyethylene glycol precipitation) and antibodies to Pseudomonas Exotoxin A (by hemagglutination) that may be important in the pathophysiology of certain infections. This study is likely to give useful information on the interaction of host and microbial factors at the onset of bacillemia, define those circumstances where granulocyte transfusions, serotherapy, or both, might be needed, yield techniques for evaluating the serologic response to infection or immunoprophylaxis, and relate the presence of circulating bacterial antigens and immune complexes to morbidity and mortality.